The action has earned the Iraqi leader the prestige that eluded him after successive victories against the Islamic State. Even some of his traditional critics have called his decision "wise" and "shrewd."

By moving forcefully, Abadi has burnished his nationalist credentials and quieted potential challengers in next year's elections who are backed by Iran and espouse policies of Shiite dominance, analysts and Iraqi politicians said.

For the United States, Abadi's surging popularity is probably the silver lining of a crisis that has pitted two of its closest political and military allies — the Iraqi government and the Kurds — against each other. Many Iraqi politicians say Abadi has all but assured his reelection next year.

"A referendum by arms," said Saad al-Muttalibi, a member of Baghdad's provincial council and a close ally of former prime minister Nouri al-Maliki, a likely challenger to Abadi in elections slated for next spring.

"The general perception is that he's indecisive in his moves," Muttalibi said. "But what he did last week proved everybody wrong, including myself. He was very decisive and very stubborn in his approach. He stuck to the law and the constitution."

It remains unclear how far Abadi is planning to go in the push to reclaim territory lost to the Kurds in 2014 as the Islamic State swept through the country. But Abadi's supporters warn that he must resume negotiations with the Kurdish authorities and keep forces away from Kurdish cities, or risk squandering the goodwill he has earned with Iraqi voters and regional powers.

"The referendum is over and now belongs to the past. We have finished it on the ground," Abadi declared last week in a rare moment of public bluster by a politician who has never quite shed the perception that he has been indecisive since he came to office in 2014.

The first test of Abadi's willingness to moderate his response to the Kurds came early Wednesday, when the Kurdish government issued a statement calling for an immediate cease-fire in exchange for "suspending" the results of the referendum and entering into negotiations with Baghdad based on constitutionally enshrined guidelines on borders and revenue sharing.

Abadi, who has said he will enter talks only if the referendum result is annulled, has not yet responded to what amounts to a precipitous comedown for the Kurdish authorities. Not engaging in talks raises the specter of further military clashes between Iraqi and Kurdish forces to control northern borders with Syria and Turkey.

Smoke rises from Iraqi security forces’ bombs as Kurdish security forces withdraw from a checkpoint in Alton Kupri, on the outskirts of Irbil, Iraq, on Oct. 20. (Khalid Mohammed/AP)

Although the military action in Kirkuk has sparked a feverish debate in Washington over waning U.S. influence as Iran asserts itself as a regional power, Iraqis have viewed it as a critical move to avoid a much-feared partition of the country.

Abadi "may have decided to ride the wave of domestic chauvinism rather than being swept aside by it," the Crisis Group wrote in a report last week.

The move has also won the support of Sunni politicians who previously expressed reservations about a second term for Abadi.

"His policies in leading the country are not entirely clear to us," said former deputy prime minister Salam al-Zaubai, citing Abadi's membership in Dawa, a Shiite Islamist party that also counts Maliki as a senior leader. "But in general we are very comfortable with what happened in Kirkuk because it was something that needed to be done long time ago."

In the weeks leading up to the Kirkuk offensive, American officials made clear that the burden fell on the Kurdish leadership to offer concessions to Abadi, who the Trump administration thought was "grievously hurt by the referendum," said one U.S. official, who spoke on the condition of anonymity to discuss private negotiations.

"Our policy is they need to do something to help Abadi. It's not starting out on an equal basis," the official said.

Trump administration officials were frustrated that the Kurds had rebuffed a proposal that U.S. officials claimed would have given the Kurdish leadership a face-saving way to postpone the referendum.

Abadi had informed U.S. diplomats of his intention to order forces into Kirkuk, but did not reveal the timing and scale of the operation, people close to Abadi said.

"This was coordinated by Mr. Abadi himself; he did not have any other choice but to move," said Mowaffak al-Rubaie, a lawmaker who sits on the security and defense committee in parliament.

As the Iraqi forces swept into Kirkuk and reclaimed its vast oil fields and municipal buildings, the United States issued conflicting responses. U.S. diplomats in Baghdad said the United States supported Iraq's right to impose federal control over contested areas, while President Trump said the United States remained neutral in the dispute.

The differing U.S. responses fueled a perception among U.S. officials and some Iraqis that Iran had superseded the United States as the most important power broker in Iraq.

The Iraqi forces who moved on Kirkuk and other places in northern Iraq included Shiite militias with ties to Tehran, fueling intense speculation of Iran's role in the campaign.

Iraqi Kurdish officials and some Iraqi politicians have concluded that Abadi acted on behalf of Iran, which fears that Kurdish independence in Iraq would provoke a similar action among its own sizable Kurdish population.

"The prime minister will take advantage of what happened, and of course it will raise his popularity in the street," said Izzat Shahbandar, a former Iraqi lawmaker. "But the reality is that [Iran] had the main role in achieving this scenario."

Shahbandar pointed to the high-profile presence of Iranian Gen. Qasem Soleimani, Iran's military point man in Iraq and Syria, in Iraq before and after the referendum vote and in the lead-up to the sweep of Kirkuk.

Kurdish officials said Soleimani brokered a deal in which peshmerga fighters from a Kurdish faction who were lukewarm on the referendum stood down when Iraqi forces entered Kirkuk.

But two people close to Abadi, who spoke on the condition of anonymity to discuss sensitive government planning, gave a different account of how it played out. They said Soleimani entered the negotiations only after Abadi and those Kurdish officials had reached the framework of an agreement. Soleimani helped persuade the Kurds to call on their forces to retreat, telling them they were vastly outnumbered.

Soleimani's interjection delayed Abadi's plan to move on Kirkuk by two days in the hopes that Kurdish President Masoud Barzani would agree to enter negotiations. The talks failed, but Soleimani's warnings were "partially helpful in convincing them to avoid bloodshed. Some of what he said had a profound impact," said a person close to Abadi who spoke on the condition of anonymity to discuss sensitive planning.

"Soleimani came in, but he was not the architect of all this," the person said.

The perception that Abadi was not in full control of the Kirkuk operation is among the many challenges he faces.

The more extremist factions of the Shiite militias are agitating for a deeper push into Kurdish territory, a move that analysts say could backfire.

U.S. Secretary of State Rex Tillerson signaled his concern about Abadi's campaign, telling the prime minister during a meeting in Baghdad on Monday that further moves toward Kurdish-held territory could provoke more armed conflict. He urged the two sides to enter serious negotiations.

Abadi has shown a willingness to take risks to turn political events to his advantage.

To the surprise of American diplomats and his own military commanders, Abadi announced a campaign to evict the Islamic State from Fallujah — a city that was seen as an impenetrable base for the group.

The Islamic State collapsed in Fallujah in about three weeks, defying forecasts of a protracted battle and forcing Sadr to call off protests. The move proved decisive in raising the morale of Iraq's security forces, which carried over to the longer and tougher battle for Mosul.

"Abadi took a big risk to get his 'rah-rah' moment, and it paid off," said a former Western diplomat. "The victory in Fallujah did bring the country together more than any other moment in recent memory."

Political opponents will be looking to exploit strategic mistakes by Abadi, said Sajad Jiyad, an analyst at the Al-Bayan Center for Planning and Studies, a think tank based in Baghdad.

"It means he has a bigger target on this back now that the perception is that he can win in a landslide," he said, "and that other Shiite groups will have less of a say in how things are done."